Comparative Evaluation of Two Antioxidants on Reversing the Immediate Bond Strength of Bleached Enamel: In Vitro Study

Abstract

BACKGROUND Tooth bleaching causes a significant decrease in the bonding strength between the resin and human enamel. Nevertheless, the effects of different antioxidant types on the immediate bonding strength of resin and bleached enamel were significantly different. Therefore, the objective of this study was to compare the effects of 2 antioxidants for enhancing the bond strength of the resin to bleached enamel. MATERIAL AND METHODS There were 48 enamel blocks performed from 48 recently extracted maxillary central incisors. There were 8 groups: NC (negative control, no bleached specimens restored without antioxidants); NA (no antioxidant, bleached specimens bonded immediately without any antioxidants); SA30, SA60, and SA120 (bleached specimens accepted the management of 10% sodium ascorbate (SA) for 30 minutes, 60 minutes, and 120 minutes, respectively, before restored); PC30, PC60, and PC120 (bleached specimens received treatment of 5% proanthocyanidins (PC) for 30 minutes, 60 minutes, and 120 minutes, respectively, before restored). We measured the micro-tensile bond strength of specimens and used 2-way ANOVA to analyze the data. RESULTS The mean±standard deviation bond strength measured were: NC, 29.99±4.00; NA, 14.90±1.97; SA30, 18.60±2.20; SA60, 22.57±2.71; SA120, 26.15±3.85; PC30, 16.78±2.29; PC60, 19.13±2.24, PC120, 23.90±2.01 MPa. In addition, the fracture types were mainly of an adhesive mode (88.75%), followed by mixed (7.5%), and cohesive (3.75%). CONCLUSIONS 10% sodium ascorbate provided a comparatively more promising improvement for immediate bond strength than 5% proanthocyanidins when the same duration of antioxidant was applied.

Figure 1

Sticks, performed with the size of 1×1×8 mm, were prepared for micro-tensile bond strength (MTBS) testing.

Figure 2

Micro-tensile bond strength (MTBS) testing was conducted at 1 mm/minute using a universal testing machine.

Figure 3

The mean value of micro-tensile bond strength in different groups was measured, with micro-tensile bond strength (MTBS) in figure representing micro-tensile bond strength.

Figure 4

Scanning electron microscopy pictures after bonding tests of all groups. (A, B) The negative control (NC) group showed that the resin-enamel interface was compact, without crack, along with the closely chimeric resin process and enamel. (C, D) The no antioxidant (NA) group demonstrated that the interface between enamel and resin cement was loose and cracked. (E, F) The sodium ascorbate at 30 minutes (SA30) showed that the interface of group 3 was denser than group 2, but there were still cracks. (G, H) The sodium ascorbate at 60 minutes (SA60) group and (I, J) the sodium ascorbate at 120 minutes (SA120) illustrated that the interface between enamel and resin was compact and crack-free, along with chimeric the resin process and enamel. (K, L) The proanthocyanidins at 30 minutes (PC30), and (M, N) the proanthocyanidins at 60 minutes (PC60) showed that the interface between enamel and resin was clear, but the band was loose. There were scattered cracks resin protrusions. (O, P) The proanthocyanidins at 120 minutes (PC120) showed that the interface between enamel and resin cement was not clear, along with the solid bond, without crack. The formation of resin protrusion could be observed.